The present invention is directed to a coal slurry and, more particularly, to an aqueous coal slurry containing dextrin as a dispersant.
Many high-intensity combustion systems require that coal be cleaned to very low levels of ash to prevent excessive wear of high-temperature, high-speed components. For these applications, the cleaned coal must contain very low levels of alkali metals in order to prevent vaporization and subsequent deposition of corrosive inorganic constituents.
When prepared as coal-water slurry fuel, the cleaned coals are often ground to a very fine particle size distribution to insure adequate combustion. The high surface area of cleaned, micronized coals can result in large demands for dispersants to achieve solids loadings suitable for specialized high-intensity combustion systems operating with coal-water slurry fuels. Because the dosages of the dispersant are generally greater than those required for coarser coal slurries for use in large industrial or utility boilers, the chemical composition of the dispersant becomes more important.
A number of different dispersants for coal-water slurry production have been utilized in the industry. An example is U.S. Pat. No. 4,088,453 wherein ammonia is added to a coal-water slurry to improve pumpability. Many other dispersants incorporate the use of polyelectrolytes and sulfonates.
Upon combustion, alkali additions resulting from the use of an alkali-containing dispersant may have marked negative effects on ash characteristics when coal has been cleaned to low ash levels. Additionally, slurry sulfur values may also noticeably increase as a result of the use of a sulfur-containing dispersant.